This invention relates to the freeze protection of solar systems, especially after the loss of externally supplied power.
A typical installation includes a solar collector, a water storage tank and interconnecting conduit means where a circulating pump circulates the water through the system. The pump is controlled by a differential control unit which senses the temperature in the collector and at the bottom of the storage tank. When the temperature in the solar collector is a predetermined number of degrees warmer than the bottom of the storage tank, the pump starts to circulate the water. When the temperature differential drops below the selected differential, the pump stops circulating the water. However, this installation can also be equipped with a freeze sensor so that when the temperature at the outlet of the solar collector drops to some predetermined value, for example, approximately 37.degree. F., the sensor activates the circulating pump and allows the warmer water in the storage tank to flow through the solar collector to prevent freezing. As the temperature rises to approximately 60.degree. F., this is sensed by the freeze sensor, and the circulating pump ceases operation and flow stops.
Another means of protecting a solar system is to drain the water from the solar collector and all conduits which could be affected by the freezing weather. After the freezing weather has left, the system can be refilled for subsequent use.
Another means used in solar water heating systems where freezing temperatures are encountered, is the use of a heat exchanger means where an antifreeze solution may be used as the heat collection fluid which is subjected to the freezing temperatures. Freeze protection means are shown in U.S. Pat. Nos. 3,986,489 and 4,019,495.